1. Field of the Invention
The present invention relates to a medical device that can remove tissue with a bolus of heated fluid.
2. Background Information
There has been developed a medical procedure commonly referred to as phacoemulsification (xe2x80x9cphacoxe2x80x9d) that is performed to remove a cataracteous lens. A phaco procedure typically involves the steps of creating an incision in the cornea and inserting an ultrasonically driven tip that breaks the lens. The tip extends from a handpiece which is held by the surgeon. The handpiece is coupled to an irrigation line and an aspiration system. The irrigation line provides an irrigation fluid to the anterior chamber of the cornea. The aspiration system pulls the irrigation fluid and emulsified lens from the cornea.
Phacoemulsification with an ultrasonic tip typically requires the breaking of the lens into relatively large pieces before emulsification into fragments that can be irrigated. Having to break the lens can be time consuming and may lead to complications in the procedure. It has been found that the lens tissue can be emulsified with a heated liquid. The heated liquid must be introduced into the cornea without burning surrounding corneal tissue such as the epithelium. Burning the epithelium may impair the vision of the patient.
U.S. patent application Ser. No. 08/755,622 U.S. Pat. No. 5,865,790 discloses a device which can emulsify lens tissue with a heated fluid. The device includes a cannula that can be inserted into the cornea. The cannula has an inner channel that is coupled to an irrigation system. A passive heating element is located within the inner channel at a distal end of the cannula. The passive heating element creates heat within the fluid under an isenthalpic process. The generation of heat occurs within the anterior chamber of the cornea at a location away from the epithelium. The heat generated by the passive heating element disclosed in the ""622 application is a continuous process. It may be desirable to provide a non-continuous process. For example, it may be desirable to generate a series of heated fluid slugs or a series of heated and non-heated fluid slugs that are directed onto the lens.
The amount of heat generated by the passive element is a function of the pressure drop across the element. The pressure drop is a function of the velocity of the fluid. The heat generated and the corresponding temperature of the irrigation fluid used to emulsify the tissue can be varied by changing the flowrate of the fluid through the cannula. Unfortunately, varying the flowrate must be upstream from the distal end of the cannula. Varying the flowrate upstream introduces a time delay between the change command and the response of the system. It may be desirable to varying the temperature essentially instantaneously. It would therefore desirable to provide a hydro-emulsifier that can generate discrete slugs of heated fluid and can quickly vary the temperature of the heated slugs.
One embodiment of the present invention includes a medical device that can emulsify tissue with a heated fluid. The device may include an active heating element that is located within an inner channel at a distal end of a cannula. The cannula is adapted to be inserted into tissue such as a cornea. The active heating element can provide heat to a fluid that flows through the inner channel.